This invention relates generally to fire detection systems and more particularly to a fire detection system using an optical spark detector. Fire detection systems are often used in textile mills or other industrial environments where flammable materials such as textile fibers are entrained in a moving air stream and thus conveyed at high speed through enclosed duct work between processing stations which perform various kinds of operations on the fibers. Infrared detectors are positioned in the duct work at intervals and are designed to detect the presence of embers or hot metal fragments in the moving air stream which could cause a fire or explosion. An infrared detector detecting a source of infrared energy in the moving air stream generates a signal which may used to activate a visual or audible alarm. The signal may also be sent to a control panel, where further signals are transmitted to instantly shut off the fiber processing equipment. Signals may also operate diverters, fire extinguishers or other equipment intended to protect life and property from a fire or explosion.
This type of system senses primarily the infrared (IR) energy generated by a glowing ember. However, the material flowing through the ducts protected by such systems generates significant static electricity which spontaneously discharges from time to time. Unfortunately, when these static electric discharges occur they radiate energy, primarily radio frequency (RF) energy, which can trigger the detector and cause an alarm. Existing spark detection systems can not distinguish between these false alarms and a true spark.
Therefore, it is an object of the invention to provide a spark detection system which is resistant to false alarms caused by static electric discharges.
It is another object of the invention to provide a detector lens which blocks radio frequency but passes infrared energy.